KR101328961B1 - Method For Transmitting And Receiving Signals In Open-Loop Spatial Multiplexing Mode - Google Patents

Method For Transmitting And Receiving Signals In Open-Loop Spatial Multiplexing Mode Download PDF

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KR101328961B1
KR101328961B1 KR1020080080461A KR20080080461A KR101328961B1 KR 101328961 B1 KR101328961 B1 KR 101328961B1 KR 1020080080461 A KR1020080080461 A KR 1020080080461A KR 20080080461 A KR20080080461 A KR 20080080461A KR 101328961 B1 KR101328961 B1 KR 101328961B1
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matrix
precoding
base station
signal
open
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KR20090098643A (en
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이문일
임빈철
천진영
고현수
이욱봉
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엘지전자 주식회사
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413MIMO systems
    • H04B7/0456Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H04B7/0486Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting taking channel rank into account
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0667Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal
    • H04B7/0671Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of delayed versions of same signal using different delays between antennas
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0682Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission using phase diversity (e.g. phase sweeping)
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0621Feedback content
    • H04B7/0634Antenna weights or vector/matrix coefficients
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04BTRANSMISSION
    • H04B7/00Radio transmission systems, i.e. using radiation field
    • H04B7/02Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0613Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission
    • H04B7/0615Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal
    • H04B7/0619Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station using simultaneous transmission of weighted versions of same signal using feedback from receiving side
    • H04B7/0636Feedback format
    • H04B7/0639Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00Baseband systems
    • H04L25/02Details ; Arrangements for supplying electrical power along data transmission lines
    • H04L25/03Shaping networks in transmitter or receiver, e.g. adaptive shaping networks ; Receiver end arrangements for processing baseband signals
    • H04L25/03891Spatial equalizers
    • H04L25/03898Spatial equalizers codebook-based design
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/26Systems using multi-frequency codes
    • H04L27/2601Multicarrier modulation systems
    • H04L27/2626Arrangements specific to the transmitter

Abstract

A method of transmitting and receiving a signal in an open-loop spatial multiplexing (SM) mode is disclosed.When the number of transmit antennas is 2 and the rank is 2 in the open-loop spatial multiplexing transmission mode, the base station is cyclic. Precoding is performed according to a delay diversity (CDD) scheme, but includes a first matrix W corresponding to an identity matrix, a second matrix D corresponding to a diagonal matrix, and a unitary matrix. The third matrix corresponding to is multiplied by a matrix (WDU) that is sequentially multiplied and then transmitted, which is substantially multiplied by the second matrix D corresponding to the diagonal matrix and the third matrix corresponding to the unitary matrix. It can be seen that the transmission is performed after precoding using the matrix DU, and the UE receives the signal by estimating the transmission scheme of the base station according to the received rank indicator and the number of transmit antennas.
Figure R1020080080461
Large Delay CDD, Open-loop SM, Identity Matrix

Description

Method for Transmitting And Receiving Signals In Open-Loop Spatial Multiplexing Mode}

The following description relates to a multi-antenna (MIMO) mobile communication system, and more particularly, to a method for efficiently transmitting and receiving signals in an open loop spatial multiplexing mode.

Recently, due to the generalization of information and communication services, the appearance of various multimedia services, and the emergence of high quality services, the demand for fast wireless communication services is rapidly increasing. To cope with this actively, the capacity of the communication system must be increased.In order to increase the communication capacity in the wireless communication environment, a method of finding new available frequency bands and increasing the efficiency of limited resources can be considered. have. Among them, the transceiver is equipped with a plurality of antennas to secure additional spatial area for resource utilization, thereby obtaining diversity gain, or transmitting data in parallel through each antenna to increase transmission capacity. The so-called multi-antenna transmit and receive technology has recently been actively developed with great attention.

Among such multiple antenna transmission / reception techniques, a multi-input multiple-output (MIMO) system using Orthogonal Frequency Division Multiplexing (OFDM) will be described as follows.

1 is a diagram illustrating a general structure of a multi-antenna transmission and reception system using OFDM.

In the transmitting end, the channel encoder 101 attaches redundant bits to the transmitted data bits to reduce the influence of the channel or noise, and the mapper 103 converts the data bit information into data symbol information, and the serial-parallel converter. 105 parallelizes the data symbols onto a plurality of subcarriers, and the multi-antenna encoder 107 converts the parallelized data symbols into space-time signals. The multiple antenna decoder 109, the parallel-to-serial converter 111, the de-mapper 113, and the channel decoder 115 at the receiving end are the multiple antenna encoder 107, the serial-to-parallel converter 105, the mapper ( 103 and the reverse function of the channel encoder 101, respectively.

In a multi-antenna OFDM system, various techniques are required to increase data transmission reliability. Among them, a space-time code (STC) scheme and a cyclic delay diversity scheme are used to increase the spatial diversity gain. Diversity (CDD) and the like, and techniques for increasing the signal-to-noise ratio (SNR) include beamforming (BF) and precoding. Here, space-time code and cyclic delay diversity are mainly used to increase transmission reliability of an open loop system in which feedback information is not available at a transmitter, and beamforming and precoding are applicable in a closed loop system in which feedback information is available at a transmitter. It is used to maximize the signal to noise ratio through the feedback information.

Among the above-described techniques, a technique for increasing the spatial diversity gain and a technique for increasing the signal-to-noise ratio, in particular, look at cyclic delay diversity and precoding as follows.

Cyclic Delay Diversity (CDD) technique is to obtain frequency diversity gain at the receiving end by transmitting all signals with different delay or different size in transmitting OFDM signals in a system having multiple transmit antennas. .

2 illustrates a configuration of a transmitting end of a multiple antenna system using a CDD technique.

OFDM symbols are separately transmitted to each antenna through a serial-to-parallel converter and a multi-antenna encoder, and then a Cyclic Prefix (CP) is attached to the receiver to prevent interference between channels. In this case, the data sequence transmitted to the first antenna is transmitted to the receiver as it is, but the data sequence transmitted to the next antenna is cyclically delayed by a certain sample compared to the antenna of the previous sequence.

On the other hand, if the cyclic delay diversity scheme is implemented in the frequency domain, the cyclic delay can be expressed as a product of a phase sequence.

FIG. 3 is a diagram for describing a method of implementing the CDD technique in the frequency domain as shown in FIG. 2.

As shown in FIG. 3, the data sequence in the frequency domain may be multiplied by a predetermined phase sequence (phase sequence 1 to phase sequence M) set differently for each antenna, and then may be transmitted to the receiver by performing fast inverse Fourier transform (IFFT). This is called a phase shift diversity technique.

Using the phase shift diversity technique, a flat fading channel can be transformed into a frequency selective channel, and frequency diversity gain can be obtained through channel codes or multi-user diversity gain can be obtained through frequency selective scheduling. have.

Precoding schemes include a codebook based precoding scheme used when the feedback information is finite in a closed loop system, and a method of quantizing and feeding back channel information. In the codebook-based precoding, a signal-to-noise ratio (SNR) gain is obtained by feeding back the index of a precoding matrix already known to the transmitting and receiving end to the transmitting end.

4 is a block diagram of a transmitter / receiver of a multi-antenna system using codebook based precoding.

Here, the transmitting end and the receiving end each have a finite precoding matrix ( P 1). ~ P L ), and the receiver feeds back the optimal precoding matrix index ( l ) to the transmitter using channel information, and the transmitter sends the precoding matrix corresponding to the fed back index to the transmission data ( χ 1 ~ χ Mt ) can be applied.

The phase shift diversity scheme or the CDD scheme may have different requirements in the open-loop and closed-loop schemes depending on whether feedback information is required. That is, it may be desirable to use different precoding matrices according to the open loop CDD scheme or the closed loop CDD scheme.

Under this assumption, it is necessary to select a suitable precoding matrix so as to obtain sufficient frequency diversity gain according to each CDD scheme and to minimize the complexity of the implementation.

An aspect of the present invention for solving the above problems is to provide a method of selecting a precoding matrix that can simplify the implementation while obtaining sufficient frequency diversity gain in various channel environments according to each transmission mode. .

In addition, an aspect of the present invention is to provide a method for efficiently transmitting and receiving a signal between the transmitting and receiving terminals according to the CDD method using the precoding matrix selected as described above.

One aspect of the present invention for solving the above problems provides a method for a user equipment (UE) to receive a signal in an open-loop spatial multiplexing (SM) transmission mode. The method includes receiving a rank indicator (RI) and antenna number information from a base station; And when the number of transmit antennas is 2, signal transmission of the base station is performed by a first matrix W corresponding to an identity matrix, a second matrix D corresponding to a diagonal matrix, and a unitary matrix. Estimating that the third matrix U corresponding to is transmitted through precoding by a matrix WDU multiplied sequentially; And receiving a signal according to the estimation of the estimating step. In this case, when the rank indicator is greater than 1, the method may further include estimating that the signal transmission of the base station is performed according to a cyclic delay diversity (CDD) scheme.

Meanwhile, another aspect of the present invention provides a method for transmitting a signal by a base station in an open-loop spatial multiplexing (SM) transmission mode. The method includes transmitting a signal according to a cyclic delay diversity (CDD) scheme when the transmission rank is greater than 1, wherein the transmitting signal is a transmission signal when the number of transmission antennas is two. Is sequentially multiplied by a first matrix W corresponding to an identity matrix, a second matrix D corresponding to a diagonal matrix, and a third matrix U corresponding to a unitary matrix. Performing precoding by matrix (WDU); And mapping the precoded signal to a resource element and transmitting the same.

In such embodiments, when the number of transmit antennas is 2 and the rank according to the rank indicator RI is 2, the second matrix D may have a form of 2 * 2. In addition, in the open-loop SMx transmission mode, the base station uses the first matrix W,

Figure 112008058642748-pat00001

It is preferable that the user equipment does not feed back a precoding matrix index (PMI) to the base station.

Meanwhile, in the above-described embodiments, when the base station transmits signals in the open loop spatial multiplexed transmission mode, when the number of transmit antennas is 2 and the transmission rank is 2, the transmission signals are transmitted according to a cyclic delay diversity (CDD) scheme. Precoding is performed by performing a precoding by a matrix DU, in which the first matrix D corresponding to the diagonal matrix and the second matrix U corresponding to the unitary matrix are sequentially multiplied, thereby precoding the precoded signal. It can also be seen as mapping and transmitting resource elements.

According to each embodiment of the present invention as described above, it is possible to simplify the implementation while obtaining a sufficient diversity gain for each transmission mode.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description, together with the accompanying drawings, is intended to illustrate exemplary embodiments of the invention and is not intended to represent the only embodiments in which the invention may be practiced. For example, the following description is given by way of specific examples applied to 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system for the sake of understanding, but the present invention is not limited to any 3GPP LTE system as well as a general multi-antenna system. The same principle can be applied to a wireless communication system. In addition, in the following description, the base station may be replaced with other terms such as "Node B" and "eNode B", and the terminal may be replaced with terms such as "user equipment" (UE) and "mobile station (MS)". Can be applied.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form around the core functions of each structure and device in order to avoid obscuring the concepts of the present invention. In the following description, the same components are denoted by the same reference numerals throughout the specification.

As described above, in one aspect of the present invention, a precoding matrix can be selected that can simplify the implementation while obtaining sufficient frequency diversity gain in various channel environments according to each transmission mode, and efficiently transmit and receive signals using the same. To provide a method. To this end, in the following, the downlink of the 3GPP LTE system described above will be described in detail for each transmission mode. Based on this, for example, the precoding matrix can be efficiently configured in the open loop spatial multiplexing transmission mode. The method of transmitting and receiving signals according to the CDD method will be described. However, the downlink of the 3GPP LTE system is exemplary only, and the present invention may be applied to other wireless communication situations.

5 is a conceptual diagram schematically illustrating a transmission process of a downlink physical channel in a 3GPP LTE system.

The codeword generated through the channel coding is performed before scrambling 501 to generate a scrambled bit block. The bit block thus generated is then generated as a modulation symbol modulated by QPSK, 16 QAM or 64 QAM by modulation mapper 502. Meanwhile, the symbols thus modulated are mapped to one or more layers by the layer mapper 503. In the 3GPP LTE system, up to two codewords can be transmitted at the same time. The two codewords are mapped to four or less layers according to predetermined criteria.

As such, precoding 504 is performed on the symbols on which the layer mapping is completed. Precoding 504 includes (1) precoding for spatial multiplexing (SM), and (2) precoding for spatial transmission diversity, and precoding for spatial multiplexing ( There is a) precoding for spatial multiplexing (SM) without the application of CDD, and (b) precoding for large delay CDD (Large Delay CDD). In the case of the open-loop spatial multiplexing transmission mode, when the transmission rank is greater than 1, the base station transmits a signal according to the CDD based precoding scheme. In addition, in a system having 2 transmit antennas (2 Tx systems), a signal is transmitted through precoding based on a fixed specific precoding matrix. In a system having 4 transmit antennas (4 Tx systems), a base station is assigned to each resource element. Signals can be transmitted by applying different precoding schemes cyclically.

Such precoded transmission symbols are mapped to appropriate resource elements by the resource element mapper 505 and then transmitted via the transmit antenna via the OFDM signal generator 506.

Meanwhile, in the precoding scheme for spatial multiplexing among the above-described precoding schemes, a scheme for reducing signaling overhead by using a specific precoding matrix in a predetermined codebook between transmitting and receiving sides is used, and among them, a precoding scheme for a large delay CDD is particularly used. The coding scheme will be described in more detail below. In addition, in the following description, precoding for a large delay CDD may be referred to as “CDD based precoding”, “CDD based precoding” or “phase shift based precoding” unless there is confusion.

CDD  base Precoding  Basic structure DU  rescue

Phase shift based precoding transmits all streams to be transmitted through the entire antenna, but multiplies the sequences of different phases. In general, when the phase sequence is generated using the cyclic delay value, the channel size becomes larger or smaller depending on the frequency domain while generating frequency selectivity in the channel when viewed from the receiver.

The phase shift based precoding matrix P can be expressed as follows.

Figure 112008058642748-pat00002

Here, k denotes a resource index, and for example, indicates an index of a subcarrier or a virtual time-frequency resource or an index of a specific frequency band.

Figure 112008058642748-pat00003
( i = 1, ..., N t , j = 1, ..., R) represents the complex weight determined by k. In addition, N t represents the number of transmit antennas, and R represents the spatial multiplexing rate. Here, the complex weight may have a different value depending on the OFDM symbol multiplied by the antenna and the index of the corresponding subcarrier. The complex weight may be determined according to at least one of channel conditions and presence or absence of feedback information.

Meanwhile, the precoding matrix P of Equation 1 is preferably designed to reduce the channel capacity loss in the multi-antenna system. To this end, the channel capacity of a multi-antenna open-loop system is expressed as follows.

Figure 112008058642748-pat00004

Here, H is a multi-antenna channel matrix of size N r x N t and N r represents the number of receiving antennas. Applying the phase shift based precoding matrix P as shown in Equation 1 to Equation 2 is as follows.

Figure 112008058642748-pat00005

As shown in Equation 3, in order to avoid loss in channel capacity, PP H must be an identity matrix, so it is preferable that the phase shift based precoding matrix P satisfies the following conditions.

Figure 112008058642748-pat00006

That is, the phase shift based precoding matrix P is preferably based on the unitary matrix.

The above-described phase shift based precoding matrix is expressed as shown in Equation 5 below for a system having an antenna number N t (N t is a natural number of 2 or more) and a spatial multiplexing rate R (R is a natural number of 1 or more). Can be. Since this can be seen as a generalized representation of the conventional phase shift diversity scheme, the multi-antenna technique according to Equation 5 will be referred to as generalized phase shift diversity (GPSD).

Figure 112008058642748-pat00007

here,

Figure 112008058642748-pat00008
Denotes the GPSD matrix for the kth resource index of the MIMO-OFDM signal having N t transmit antennas and a spatial multiplexing rate of R,
Figure 112008058642748-pat00009
The
Figure 112008058642748-pat00010
It is a unitary matrix (second matrix) that satisfies Δ is used to minimize interference between subcarrier symbols corresponding to each antenna. In particular, in order to maintain the unitary matrix characteristic of the diagonal matrix (first matrix; D) for phase shifting,
Figure 112008058642748-pat00011
It is desirable that the self also satisfies the condition of the unitary matrix.

In Equation 5, the phase angles θ i , i = 1, ..., N t in the frequency domain have the following relationship with the delay time τ i , i = 1, ..., N t in the time domain.

Figure 112008058642748-pat00012

Here, N fft represents the number of subcarriers of the OFDM signal.

As shown in Equation 5, the precoding matrix defined in the form of the product of the first matrix corresponding to the diagonal matrix D and the second matrix corresponding to the unitary matrix U is hereinafter referred to as "CDD-based precoding. It will be referred to as the "basic structure" or "DU structure".

Generalized Phase Transition Diversity  expansion - PDU Of WDU  rescue

In the above-described embodiment of the DU structure, a matrix P corresponding to a precoding matrix selected from a predetermined codebook between the transmitting and receiving sides is included in the basic structure of the CDD based precoding composed of the diagonal matrix D and the unitary matrix U. In addition, extended CDD-based precoding matrices can be constructed. This can be expressed as follows.

Figure 112008058642748-pat00013

The extended CDD-based precoding matrix is characterized in that a precoding matrix P having a size of N t x R is added before the diagonal matrix, and thus the size of the diagonal matrix is changed to R x R, compared to Equation 5. . The added precoding matrix (

Figure 112008058642748-pat00014
) May be set differently for a specific frequency band or a specific subcarrier symbol, and it is preferable that the open loop system is set to use a fixed specific matrix as described above. Such a precoding matrix (
Figure 112008058642748-pat00015
In addition, a more optimized signal-to-noise ratio (SNR) gain can be obtained.

In addition, the added precoding matrix may be designated as "W" as a matrix selected from the codebook of the 3GPP LTE system.

Hereinafter, as described above, the extended CDD-based precoding matrix will be referred to as a "PDU structure" or "WDU" structure.

Codebook subset restriction technique

In the 3GPP LTE system, a codebook preset between a transmitting and receiving end is as follows for 2 Tx and 4 Tx.

Figure 112008058642748-pat00016

Figure 112008058642748-pat00017

Table 1 shows a codebook used in a 2 Tx system, and Table 2 shows a codebook used in a 4 Tx system.

Meanwhile,

Figure 112008058642748-pat00018
There may be a case in which a codebook including two precoding matrices is used by applying a codebook subset restriction scheme using only a portion of a codebook according to a base station or a terminal. in this case,
Figure 112008058642748-pat00019
Precoding matrices
Figure 112008058642748-pat00020
It can be shortened to the number of precoding matrices. Here, the codebook subset limiting technique may be used to reduce multi-cell interference or to reduce complexity. here
Figure 112008058642748-pat00021
Assume that the conditions of For example, the total number of precoding matrices in a codebook
Figure 112008058642748-pat00022
Is a complete set of codebooks
Figure 112008058642748-pat00023
And, for example, a codebook determined to use only four precoding matrices out of six precoding matrices
Figure 112008058642748-pat00024
Can be expressed as Equation 8 below.

Figure 112008058642748-pat00025

Figure 112008058642748-pat00026

In Equation (8)

Figure 112008058642748-pat00027
The
Figure 112008058642748-pat00028
Equivalent codebook that rearranges the index of the codebook.

Meanwhile, if a precoding matrix set defined in a transmission / reception period at a specific time is defined in advance, it may be expressed as in Equation (9).

Figure 112008058642748-pat00029

Figure 112008058642748-pat00030

In Equation 9, the set of precoding matrices is

Figure 112008058642748-pat00031
It contains two precoding matrices. Equation 9 above may be simplified to a form as shown in Equation 10 below.

Figure 112008058642748-pat00032

Figure 112008058642748-pat00033

That is, Equations 8 and 9 represent codebooks.

Figure 112008058642748-pat00034
The precoding matrices within the loop are repeatedly used according to subcarriers or resource indexes. And, in Equation 10 above
Figure 112008058642748-pat00035
Is a mix of data streams,
Figure 112008058642748-pat00036
May be referred to as a data stream substitution matrix and may be selected according to the spatial multiplexing rate R as shown in Equation 9.
Figure 112008058642748-pat00037
Can be expressed in a simple form as shown in Equation 11 below.

Spatial Multiplexing Rate 2

Figure 112008058642748-pat00038

Spatial Multiplexing Rate 3

Figure 112008058642748-pat00039

Spatial Multiplexing Rate 4

Figure 112008058642748-pat00040

The method of cyclically repeating the precoding matrices in the above-described codebook may be used in the codebook to which the codebook restriction technique is applied. For example, the equation

Figure 112008058642748-pat00041
Applying Equation 10 may be expressed as Equation 12 below.

Figure 112008058642748-pat00042

Figure 112008058642748-pat00043

K in Equation 12 above represents a resource index and

Figure 112008058642748-pat00044
to be. That is, Equation 12 represents a codebook in which the precoding matrix is limited.
Figure 112008058642748-pat00045
The precoding matrices within the loop are repeatedly used according to subcarriers or resource indexes.

On the other hand, in the case of performing CDD based precoding using the full rank in the 2 Tx system using the open loop spatial multiplexing transmission mode as described above, since the sufficient frequency diversity gain can be obtained due to the large delay CDD itself, It is preferable to fix the coding matrix W to any one because it can simplify the implementation. Therefore, in the following embodiments, a method of selecting a preferred precoding matrix when performing CDD based precoding based on the fixed precoding matrix will be described.

Open loop  Spatial multiplexing In mode CDD  base Precoding  Way

Large delay CDD precoding in the open loop SM mode may be performed according to the PDU structure or the WDU structure as shown in Equation 7 above. In order to explain the above-described circular application concept, it is expressed as follows.

Figure 112008058642748-pat00046

here,

Figure 112008058642748-pat00047
Represents the number of precoding matrices in the codebook subset,
Figure 112008058642748-pat00048
Denotes the number of consecutive resource elements RE using the same precoding matrix, and i denotes the resource index as k. Therefore, the precoding matrix is
Figure 112008058642748-pat00049
Are used per resource index,
Figure 112008058642748-pat00050
Precoding matrices may be used cyclically. Further details on the open-loop large delay CDD scheme are as follows.

(1) The precoding matrix index (PMI) is not used.

(2) in 2 Tx system

Figure 112008058642748-pat00051
Is set to one.

(3) in 4 Tx system

Figure 112008058642748-pat00052
Is set to 4, and regardless of the rank, {12, 13, 14, 15} of Table 2 is used.

(4) The open loop large delay CDD scheme is applied only when the rank is larger than one, and the transmit diversity scheme is used for the rank one.

(5) Dynamic rank adaptation is possible between the transmit diversity scheme and the open loop SM scheme.

In the case of a 4 Tx antenna, only four of the sixteen matrices defined in Table 2 above are used, regardless of rank, to obtain sufficient diversity gain while reducing decoding complexity. However, in the case of the 2 Tx open loop SM, only one of three matrices for rank 2 is used in Table 1 above. Therefore, it is very important to correctly select a matrix used in such a case, and this embodiment proposes a method of selecting a precoding matrix for large delay CDD based precoding in the 2 Tx open loop SM scheme.

First, considering the case of rank 2 in Table 1 as follows.

Figure 112008058642748-pat00053

In Equation 14, when the index 1 and the index 2 are combined with a large delay CDD, a similar function is performed as an identity matrix for performing column switching. However, when the index 0 precoding matrix is used for large delay CDD based precoding, the open loop SM functions as a DFT matrix for performing heat exchange, thereby obtaining a higher SNR gain in a good correlation channel. Can be. Accordingly, in a preferred embodiment of the present invention, the first matrix W and the diagonal matrix corresponding to the unit matrix of index 0 in Equation 14 above are precoded when the rank is 2 in the open-loop spatial multiplexed transmission mode 2 Tx. It is proposed to transmit a signal by performing precoding by a matrix (WDU or PDU) that is sequentially multiplied by a second matrix D corresponding to and a third matrix U corresponding to a unitary matrix. When the matrix of index 0 is used as the first matrix W, the present inventors performed a simulation as follows about what performance difference is shown compared to the case of using the index 1 or 2.

<Simulation Result>

As described above, in the case of using index 1 of Equation 14 and index 2 in open-loop CDD-based precoding, similar performances are shown. In the present simulation, W in the WDU structure is represented by index 0 of Equation 14. The comparison is made only for the case of using the index and the case of using the index 1. In this simulation, we compared the performance of 2 Tx open loop SM according to rank 2 matrix index, MCS level and channel mode. In addition, it is assumed that a high time varying channel is generally used for long-term link adaptation of a distributed transmission mode to provide robustness under a fast channel update environment. Table 3 below shows the remaining assumptions of this link level simulation.

Figure 112008058642748-pat00054

FIG. 6 is a graph comparing performance when using index 0 and index 1 for rank 2 of a 2 Tx codebook for an open loop SM under an ITU-PedA channel.

As can be seen from FIG. 6, it can be seen that the use of index 0 and the use of index 1 in an uncorrelated spatial channel do not show much difference in performance. However, under a high correlation channel, it can be seen that the use of index 0 for rank 2 of the 2 Tx codebook shows a significant performance improvement over the case of using index 1 according to the present embodiment. This can be seen because the DFT matrix forms a beam and provides an SNR gain by averaging the two beams. In addition, when a high modulation level is used, it can be confirmed that the use of index 0 for rank 2 of the 2 Tx codebook shows higher performance improvement according to the present embodiment.

FIG. 7 is a graph comparing performance when using index 0 and index 1 corresponding to rank 2 in a 2 TX codebook for an open loop SM under a 6-Ray TU channel.

That is, FIG. 7 shows a performance comparison similar to that of FIG. 6 except for the channel mode. As can be seen from FIG. 7, it can be seen that the use of index 0 according to the present embodiment provides a better performance gain even under a rich frequency diversity channel.

The above description is summarized as a method for receiving a signal from a base station by a terminal in one aspect of the present invention. In the open loop spatial multiplexing transmission mode, when the terminal receives a signal, the terminal first receives a rank indicator (RI) from the base station through downlink control information. If the received rank indicator is 1, the UE transmits a signal according to the transmit diversity scheme, and if the rank indicator is greater than 1, the UE assumes that the base station transmits a signal according to the CDD scheme.

If the rank indicator is greater than 1, that is, the base station transmits a signal according to the CDD scheme, the reception scheme may vary depending on the case where the number of transmission antennas is two and four. In the case of 4 Tx, the UE estimates that precoding is performed by cyclically applying four precoding matrices of the 16 codebooks to P or W of the PDU / WDU structure as described above, and receives a signal. Meanwhile, in the case of 2 Tx, the UE estimates that the base station performs precoding by applying the unit matrix corresponding to index 0 of Equation 14 to P or W of the PDU / WDU structure and receives a signal. According to the estimation result, the terminal receives a signal.

In the case of 2 Tx rank (R) 2 of the above scheme, the diagonal matrix portion of the PDU / WDU structure has a 2 * 2 form. That is, since the unit matrix is used as "P" or "W" in the PDU / WDU structure, and the number of transmit antennas and the number of ranks are the same, the CDD-based precoding base matrix or the DU structure of the above-described embodiments is substantially the same. It can also be seen as an application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The foregoing description of preferred embodiments of the invention disclosed herein has been presented to enable any person skilled in the art to make and use the invention. While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims It can be understood that Accordingly, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

According to the signal transmission / reception method according to each embodiment of the present invention as described above, it is possible to efficiently select the precoding matrix according to each transmission mode to obtain a sufficient diversity gain, so as not to complicate the implementation. This approach can be applied according to the same principle to the above-mentioned 3GPP LTE system as well as any multi-antenna communication system using CDD based precoding.

1 is a diagram illustrating a general structure of a multi-antenna transmission and reception system using OFDM.

2 illustrates a configuration of a transmitting end of a multiple antenna system using a CDD technique.

FIG. 3 is a diagram for describing a method of implementing the CDD technique in the frequency domain as shown in FIG. 2.

4 is a block diagram of a transmitter / receiver of a multi-antenna system using codebook based precoding.

5 is a conceptual diagram schematically illustrating a transmission process of a downlink physical channel in a 3GPP LTE system.

FIG. 6 is a graph comparing performance when using index 0 and index 1 for rank 2 of a 2 Tx codebook for an open loop SM under an ITU-PedA channel.

FIG. 7 is a graph comparing performance when using index 0 and index 1 corresponding to rank 2 in a 2 TX codebook for an open loop SM under a 6-Ray TU channel.

Claims (12)

  1. A method for receiving a signal by a user equipment (UE) in an open-loop spatial multiplexing (SM) transmission mode,
    Receiving the number information of the transmit antennas from the base station; And
    Assuming that a precoded signal is transmitted using a matrix for transmitting a signal in an open-loop spatial multiplexing (SM) mode of a transmitting antenna, receiving a signal from the base station Including,
    The matrix is a matrix WDU in which the first matrix W, the second matrix D corresponding to the diagonal matrix, and the third matrix U corresponding to the unitary matrix are sequentially multiplied.
    The user equipment determines that the base station using the open-loop spatial multiplexing mode of the two transmit antennas uses the first matrix W in the matrix as a unitary matrix for large delay delay cyclic delay diversity (CDD) based precoding. Characterized in that it is assumed to use a fixed identity matrix),
    How to receive the signal.
  2. The method of claim 1,
    The second matrix D is
    When the number of transmit antennas is 2 and the transmission rank (Rank) is 2, it has a 2 * 2 form, the signal receiving method.
  3. The method of claim 1,
    The user device,
    In an open-loop SM multiplex mode of the two transmit antennas, the base station decodes the first matrix W of the matrix for the large delay CDD precoding.
    Figure 112012071011759-pat00064
    Assume that it is fixed to use,
    And the user equipment does not feed back a precoding matrix index (PMI) to the base station.
  4. In a method for transmitting a signal by a base station in an open-loop spatial multiplexing (SM) transmission mode,
    Precoding a signal using a matrix for large delay cyclic delay diversity (CDD) based precoding in an open loop spatial multiplexing mode of a two transmit antenna;
    Mapping the precoded signal to resource elements; And
    Transmitting the mapped signal to a user equipment (UE);
    The matrix is a matrix WDU in which the first matrix W, the second matrix D corresponding to the diagonal matrix, and the third matrix U corresponding to the unitary matrix are sequentially multiplied.
    The base station using the open-loop spatial multiplexing mode of the two transmit antennas is characterized in that the first matrix (W) in the matrix is fixed to use an identity matrix for large delay CDD based precoding. ,
    Signal transmission method.
  5. 5. The method of claim 4,
    The second matrix D is
    When the number of transmit antennas is 2 and the transmission rank (Rank) is 2, it has a 2 * 2 form.
  6. 6. The method of claim 5,
    In the open loop spatial multiplexing mode of the two transmit antennas, the base station decodes the first matrix W of the matrix for the large delay CDD precoding.
    Figure 112012071011759-pat00065
    Fixed to
    And a precoding matrix index (PMI) is not fed back from the user equipment.
  7. A user equipment (UE) for receiving a signal from a base station in a wireless communication system,
    A precoded signal was transmitted using a matrix for receiving information on the number of transmit antennas from the base station and transmitting a signal in an open-loop spatial multiplexing (SM) mode of two transmit antennas. A receiving module for receiving a signal from the base station assuming;
    The matrix is a matrix WDU in which the first matrix W, the second matrix D corresponding to the diagonal matrix, and the third matrix U corresponding to the unitary matrix are sequentially multiplied.
    The user equipment determines that the base station using the open-loop spatial multiplexing mode of the two transmit antennas uses the first matrix W in the matrix as a unitary matrix for large delay delay cyclic delay diversity (CDD) based precoding. Characterized in that it is assumed to use a fixed identity matrix),
    User device.
  8. The method of claim 7, wherein
    The second matrix D is
    If the number of the transmission antenna is 2 and the transmission rank (Rank) is 2, the user device having a form of 2 * 2.
  9. The method of claim 7, wherein
    The user device,
    In an open-loop SM multiplex mode of the two transmit antennas, the base station decodes the first matrix W of the matrix for the large delay CDD precoding.
    Figure 112012071011759-pat00066
    Assume that it is fixed to use,
    The user equipment does not feed back a precoding matrix index (PMI) to the base station.
  10. A base station for transmitting a signal to a user equipment (UE) in a wireless communication system,
    A precoder for precoding a signal using a matrix for large delay Large Delay cyclic delay diversity (CDD) based precoding in an open-loop spatial multiplexing (SM) mode of two transmit antennas;
    A mapper for mapping the precoded signal to resource elements; And
    A transmitting module for transmitting the mapped signal to the user equipment,
    The matrix is a matrix WDU in which the first matrix W, the second matrix D corresponding to the diagonal matrix, and the third matrix U corresponding to the unitary matrix are sequentially multiplied.
    The base station using the open-loop spatial multiplexing mode of the two transmit antennas is characterized in that the first matrix (W) in the matrix is fixed to use an identity matrix for large delay CDD based precoding. ,
    Base station.
  11. 11. The method of claim 10,
    The second matrix D is
    When the number of transmit antennas is 2 and the transmission rank (Rank) is 2, the base station having a 2 * 2 form.
  12. 11. The method of claim 10,
    In the open loop spatial multiplexing mode of the two transmit antennas, the base station decodes the first matrix W of the matrix for the large delay CDD precoding.
    Figure 112012071011759-pat00067
    Fixed to
    And not receiving a precoding matrix index (PMI) from the user equipment.
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